The present invention relates to a portable data collection device including an imaging based dataform reader and, more particularly, to a portable data collection device including an imaging based dataform reader utilizing a multi-cuspid mirror arrangement to increase apparent resolution of a photosensor.
Portable data collection devices are widely used in manufacturing, service and package delivery industries to perform a variety of on-site data collection activities. Such portable data collection devices often include integrated bar code dataform readers adapted to read bar code dataforms affixed to products, product packaging and/or containers in warehouses, retail stores, shipping terminals, for inventory control, tracking, production control and expediting, quality assurance and other purposes.
Bar code dataforms come in a variety of different formats including one and two dimensional bar codes, matrix codes and graphic codes, as well as words and numbers and other symbols, which may be printed or etched on paper, plastic cards and metallic and other items. For example, a one dimensional bar code dataform typically consists of a series of parallel light and dark rectangular areas of varying widths. The light areas are often referred to as xe2x80x9cspacesxe2x80x9d and the dark areas as xe2x80x9cbarsxe2x80x9d. Different widths of bars and spaces define different characters in a particular bar code dataform.
Data originally encoded in a dataform is recovered for further use in a variety of ways. For example, a printed bar code may be illuminated to derive reflectance values which are digitized, stored in buffer memory and subsequently decoded to recover the data encoded in the bar code. The printed bar code may be illuminated using a laser, an array of LEDs, ambient light, or the like. The light reflected from the printed bar code typically is captured using a photosensor such as, for example, a CCD detector or CMOS detector.
A problem associated with conventional dataform readers is that the readers are designed to read dataforms located within a limited range therefrom. For example, a dataform reader may be designed to read dataforms located within the range of three inches to twelve inches from the reader. The maximum distance at which a dataform reader is able to read a dataform is limited by a resolution of the photdetector used to capture the dataform. For example, using a conventional 640 horizontal pixel photosensor, one dimensional bar code dataforms can be read so long as the distance the reader is placed from the dataform is such that the 640 horizontal pixels are suitable to distinguish among the narrowest bars and spaces forming the dataform. As the dataform reader is moved further away from a dataform, the images of the bars and spaces appear smaller at the photosensor thereby limiting the range at which the dataform reader is able to read a dataform.
One way to allow the dataform reader to read the dataform at longer distances is to increase the resolution of the photosensor. For example, rather than providing 640 horizontal pixels, the photosensor may include 1000 or more horizontal pixels. In this manner, the photosensor is able to distinguish among smaller features of the dataform thereby enabling reading of dataforms located farther away. A significant drawback to increasing the number of horizontal pixels on the photosensor is that a width of the photosensor becomes proportionately larger in order to accommodate the additional pixels. As the width of the photosensor increases, so does the overall width of the reader module. Unfortunately, due to customer demand for smaller and more compact dataform readers, the ability to increase the width of the reader module is often not a feasible option.
Accordingly, there is a strong need in the art for a dataform reader which is capable of reading dataforms at longer distances which overcomes the afore mentioned drawbacks.
In accordance with one aspect of the present invention, a range at which a dataform reader is able to read a dataform is improved by increasing an apparent resolution of a photosensor capturing the image of the dataform. The apparent resolution of the photosensor is increased by providing a reader module having two or more mirrors and a single lens with partially overlapping fields of views. Each field of view is set to capture a respective portion of a full dataform image. For instance, the field of view from each mirror may be set to capture a respective portion of a one-dimensional bar code label.
In order to increase the apparent resolution of the photosensor, each of the mirrors is preferably arranged to focus a respective image of the dataform onto different zones of the photosensor. For instance, each mirror may be arranged to direct images onto rectangular shaped zones arranged vertically with respect to one another. Upon capturing an image from the lens in different zones, the fill image of the dataform is reconstructed. In particular, the images from each zone is preferably provided to an image processor whereby overlapping data from each zone is accounted for and a single image representative of a combined field of view from the lens and mirrors is obtained. Since an image from each mirror is focused onto different zones and then combined, the apparent resolution of the photosensor is increased. For instance, if a multiple mirror dataform reader has a two-dimensional photosensor with 640 horizontal pixels and the mirrors are arranged to project respective images on three different rectangular zones of the photosensor, the apparent horizontal resolution of the photosensor increases from 640 pixels to 1920 (640xc3x973) pixels less the number of pixels providing overlapping data in each zone. It will be appreciated that since the photosensor itself need not be increased in width to accommodate such higher horizontal resolution imaging, the overall width of the reader module may remain unchanged. Thus, the dataform reader is able to read dataforms at longer ranges by increasing the apparent resolution of the photosensor, without increasing the overall width of the reading module itself.
According to one aspect of the invention, a dataform reading module, is provided. The dataform reading module includes at least one photosensor providing a plurality of different zones for image capture, a lens for focusing a respective image representing a portion of a dataform taken along a target line onto a respective one of the plurality of different zones, at least two mirrors configured to direct an image of adjacent and partially overlapping portions of the dataform taken along the target line onto the lens, and an illuminating device for illuminating the dataform.
According to another aspect of the invention, a dataform reader for reading a dataform is provided. The dataform reader includes a hand-portable sized housing having at least one lens, a reading module included within the housing, the reading module including, a photosensor array having a plurality of different zones, a plurality of mirrors for directing a respective image representing a portion of the dataform along a target line onto a respective one of the plurality of different zones, at least one lens configured to focus an image of adjacent and partially overlapping portions of the dataform along the target line, and an illuminating device for illuminating the dataform.
According to yet another aspect of the invention, a method for reading a dataform employing a dataform reading module is provided. The method includes the steps of focusing a plurality of images of a dataform onto respective zones of a photosensor array from at least two mirrors, at least two of the images received from the at least two mirrors corresponding to adjacent and partially overlapping segments of the dataform taken along a target line, and reconstructing a final image of the dataform taken along the target line from a combination of the plurality of images provided to the respective zones.
According to still yet another aspect of the invention, a dataform reading module is provided. The dataform reading module including means for capturing images of a dataform, means for receiving images of adjacent portions of the dataform onto respective different regions of the means for capturing; and means for combining the images of the adjacent portions to a single image of the dataform.
These and other aspects, features and advantages of the invention will become better understood from the detailed description of the preferred embodiments of the invention which are described in conjunction with the accompanying drawings.